Compression test readings question
Post Fiend
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From: Missouri
Compression test readings question
You want your readings to be within 75% of eachother. The actual amount of cranking pressure only matters if is is really low. A 12:1 race engine may have less cranking pressure than a 9:1 truck engine.
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From: Eureka, Ca.
Compression test readings question
That should be 10-15 Percent. Take your highest reading and multiply by .15 then subtract the result from the highest reading.
Ex. 150psi x .15 =22.5 150-22.5 = 127.5 So if your highest reading is 150 then none of your other readings should be below 127.5
Ex. 150psi x .15 =22.5 150-22.5 = 127.5 So if your highest reading is 150 then none of your other readings should be below 127.5
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Senior User
Joined: Jan 2002
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From: Las Vegas
Compression test readings question
Thanks for getting back to me.
Now, what psi should I be looking for? 150?
What is considered high enough?
What is considered too low?
Thanks again.
Hawkeye
Now, what psi should I be looking for? 150?
What is considered high enough?
What is considered too low?
Thanks again.
Hawkeye
Post Fiend
Joined: Feb 2000
Posts: 5,130
Likes: 8
From: Brea CA
Compression test readings question
Here's the specs out of the '68 service manual:
Compression Pressure 120 - 160psi
Allowable Variation Between Cylinders 20psi
Not to start anything but I think the 75% rule is ok as long as none are under 100psi.
Barry
Compression Pressure 120 - 160psi
Allowable Variation Between Cylinders 20psi
Not to start anything but I think the 75% rule is ok as long as none are under 100psi.
Barry
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Senior User
Joined: Jan 2002
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From: Las Vegas
Compression test readings question
Thanks a bunch Barry. Also to the others that replied.
That's what I needed to know. Now I'll go check to see what I get.
Hawkeye
That's what I needed to know. Now I'll go check to see what I get.
Hawkeye
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Elder User
Joined: Apr 2002
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From: Texas Hill Country
Compression test readings question
Originally posted by BB
Here's the specs out of the '68 service manual:
Compression Pressure 120 - 160psi
Allowable Variation Between Cylinders 20psi
Not to start anything but I think the 75% rule is ok as long as none are under 100psi.
Barry
Here's the specs out of the '68 service manual:
Compression Pressure 120 - 160psi
Allowable Variation Between Cylinders 20psi
Not to start anything but I think the 75% rule is ok as long as none are under 100psi.
Barry
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Senior User
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From: Las Vegas
Compression test readings question
Test Warm w/o oil added into the cylinders.
1. 175
2. 165
3. 165
4. 170
5. 165
6. 170
7. 168
8. 170
These readings look pretty good to me.
My engine has a year and a half on the rebuild.
It has been smoking some recently. Mostly black smoke with a tinge of blue. When I smogged it the guy told me it was a little rich. This week I found a vacumm leak at the tree at the rear of the intake manafold. also I had the pcv hooked up to that instead of the port on front of my edelbrock carb.
I changed out the tree and rerouted the pcv and have a great improvment in the smoke. Also I had been pinging a fair amount as well. That cleared up too.
The engine has been a hog on oil consumption, as much as a quart every week and a half, I'm trying to address that as well. It looks like the lower end is okay, so now I'll be looking into other areas. Also I'm suffering from low oil preasure, I don't know if the oil mods were done to my block, when I had the engine done it was before I had read about them here on the site.
Any comments or ideas are gladly accepted.
Thanks,
Hawkeye
1. 175
2. 165
3. 165
4. 170
5. 165
6. 170
7. 168
8. 170
These readings look pretty good to me.
My engine has a year and a half on the rebuild.
It has been smoking some recently. Mostly black smoke with a tinge of blue. When I smogged it the guy told me it was a little rich. This week I found a vacumm leak at the tree at the rear of the intake manafold. also I had the pcv hooked up to that instead of the port on front of my edelbrock carb.
I changed out the tree and rerouted the pcv and have a great improvment in the smoke. Also I had been pinging a fair amount as well. That cleared up too.
The engine has been a hog on oil consumption, as much as a quart every week and a half, I'm trying to address that as well. It looks like the lower end is okay, so now I'll be looking into other areas. Also I'm suffering from low oil preasure, I don't know if the oil mods were done to my block, when I had the engine done it was before I had read about them here on the site.
Any comments or ideas are gladly accepted.
Thanks,
Hawkeye
Last edited by Hawkeye58; Sep 3, 2003 at 09:35 PM.
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